Flow line systems which transport potentially dangerous fluids, such as propane, liquid petroleum gas, or anhydrous ammonia, often include a separable connection for emergency interruption of the flow line extending between a stationary vessel and a portable vessel. Occasionally a transport vehicle pulls away from a stationary filling platform prior to disconnecting one or more flexible fill lines, and the absence of a separable connection may otherwise cause a rupture of the filling station storage tank, which typically has a large capacity. The monetary loss of fluid from such a rupture is nominal compared to the risks commonly associated with the release of toxic vapors, to the environmental consequences of polluting the filling station site, and/or to the fire hazard associated with such a rupture.
A separate connection is often designed into the flow line or fill line to form a "weak link", so that this connection breaks in response to bending forces before the rupture of other potions of the fluid system, such as the holding tank. One commonly used filling system designed to create a weak link connection utilizes a steel bulkhead encased in concrete and enclosing a portion of the flow line extending between the holding tank and a swivel for a flexible line which is passed to the transport vehicle, thereby ensuing that the flow line will break downstream from the concrete bulkhead during an inadvertent vehicle pullaway. This bulkhead system is expensive, particularly if this technique is used to retrofit an existing filling station. Another type of weak link system, referred to as the PASS system, utilizes a shear fitting or coupling mounted within a vertical portion of the flow line. The shear fitting is designed to break in response to lateral forces transmitted through the flexible line during the inadvertent pullaway. The PASS system, which has been applied to anhydrous ammonia filling stations, is also complicated and expensive. The PASS system similarly cannot readily be adapted to retrofit an existing filling station, and has other disadvantages described below.
In each of the above "weak link" systems, a shutoff valve may be installed upstream from the separable connection to retain the fluid in the holding tank if the fill line is broken. The American National Standards and Compressed Gas Association requires all stationary storage installations to have an emergency shutoff valve mounted immediately upstream from the location in the fluid flow system where the flexible hose swivel is mounted, so that a rupture occurring on the flexible hose side of the system can be shut in by this emergency valve. An "excess flow" valve would thus typically be installed in the rigid line downstream from the steel and concrete bulkhead and immediately upstream from the hose swivel. An "excess flow"valve will only terminate flow, however, if there is a rupture in the system which causes the flow rate to exceed the anticipated fill rate, and a leak or rupture may occur downstream from an excess flow valve which does not result in valve closing since the flow rate caused by the rupture does not exceed this preselected value. The PASS system includes an emergency shutoff valve upstream from the shear fitting, with this valve being connected by a tether line extending to the flow line downstream from the shear fitting, so that tension in this line during a pullaway hopefully actuates the shutoff valve to the closed position.
Other types of separable connections include various types of inline valves which separate in response to pullaway forces transmitted through the flexible flow line. One type of inline connection promoted by Rego Products utilizes a form of quick disconnect, with an outer sleeve of the connection being tethered to a stationary point upstream from the valve. When tension is applied to the tether line during the pullaway, the valve is initially pulled away from this fixed point, thereby creating tension on the tether line and subsequently pulling the sleeve axially backward to separate the connection. Another type of inline connection utilizes a shear coupling within a flow line valve, and a shear member is broken by the flow line tension caused during inadvertent pullaway. Each of these latter systems include valves in each coupling housing designed to stop fluid flow in either direction from the disconnected connection. The latter shear coupling design has been applied to a conventional vehicle fueling system, as disclosed in U.S. Pat. No. 4,899,792. U.S. Pat. No. 3,874,428 discloses a gas filling system which includes an excess flow valve and check valves. U.S. Pat. Nos. 4,354,522 and 4,998,560 each disclose complicated emergency shut off systems which are expensive, and are not readily adaptable to common anhydrous ammonia or propane filling stand sites.
A significant problem with the above-described systems in operation is that the separation force exerted on either the "weak link" connection or the inline connection during a pullaway depends upon the pullaway direction. The driver may pull a portable container from a filling station in any direction within an are of 180 degrees or more, and during this pullaway the flexible flow line can easily engage and become partially wrapped around one or more stationary components, thereby significantly altering the forces required to cause the break or separation in the system. The flexible flow line extending between the swivel and the discharge nozzle may not have a uniform outer diameter, and a coupling, check valve, or various other components secured to or located along the flexible line may also get hung up on a stationary member during pullaway, thereby again significantly affecting the force required to break or separate the system at the intended connection, and possibly causing a rupture at an unintended location within the flow system. It should further be understood that tether lines or cords extending from one component to a safety shutoff valve or disconnect may engage various stationary or portable components, thereby also adversely affecting the reliability of the system. A tether line may become wrapped about or snagged upon a stationary support, the flexible flow line, a broom, or various other objects, so that the reliability of a system utilizing a tether line depends upon system installation procedures and operator discretion.
Another significant problem with prior art flow line disconnect techniques is that the systems do not easily and reliably allow for adjusting the force required to separate or uncouple the connection. The "weak link" systems can only be effectively adjusted by replacing the weak link member, and springs or other biasing components within the inline connections must be replaced to adjust the force required to uncouple the connection. Field adjustment of such system is thus impractical and is limited to specific values determined by on-hand replaceable components. Many of the prior art systems cannot be effectively retro fitted to existing filling stations of the type commonly used for anhydrous ammonia or propane filling sites. Many prior art systems are expensive, and the substantial effort required to repair a disconnected system encourages filling station operators to deactivate the system. Moreover, the reliability of the existing systems is significantly affected by the direction of pullaway, which the filling station operator cannot effectively control. As a consequence, many filling station sites continue to employ the crude control of a steel and cement bulkhead and an excess flow valve, leaving the site operator exposed to significant contamination and safety risks.
The disadvantages of the prior art are overcome by the present invention, and an improved safety connection is hereinafter disclosed for a fluid flow system. The connection of the present invention may be employed in various flow lines extending between a stationary and a portable container, and is particularly well adapted for use at a conventional anhydrous ammonia, liquid petroleum gas, or propane filling site.